Production of magnesium chloride



Aug. 16, 1949. w. E. BRKE Er Al.

PRODUCTION OF MAGNESIUM CHLORIDE Filed may 29, 1944 3 Sheets-Sheet 1 mOjOm m0303303. H65@ Ezmuzoo NllJ mwN-

Aug. 16, 1949.

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Jal/W Patented Aug. 16, 1949 Y UNITED s'm'rlzs k'PATintl"foi-"Fice I PRODUCTION F lVlAGrNESIUANIV j William E. Burke and William A. Smith, Carlsbady Y' "l N. Mex., and Paul D. assignors to Internatio Corporation, a corpora Application May 29, 1944, Serial No.

3 Claims. (C1. 23,-.-9U

, '1 Our invention relates to improvements in the production of magnesium chloride from` an aqueous solution containing notonly magnesium and chlorine ions, but also undesired substances such as potassium, sodium and sulphate ions.

For certain purposes, for example when used as a feed Vfor electrolyticcells employed in the production of magnesium metal, the magnesium chloride should bel of high purity, and particularly it should contain the minimum amount of sulphate, because sulphate islvery undesirable from the standpoint of satisfactory operation of the electrolytic cells usedY inrthe production of magnesium metal. However, containing magnesium frequently alsorcontain sulphates in addition to other substances.Y For instance, the magnesium-containing minerals such as are found in the Carlsbad, New Mexico,

or othersimilar mineral deposits containV maigy nesium principally in the form of Langbeinite (2MgSO4.K2SO4) Kainte (KC1.MgSO4.3H2O) 01 KieseriteV (MgSO4-H2O) Also, as is usual in thelc'ase of minerals olo-Y tained from such deposits, other undesirable materials are present in the ores, for example Halite (NaCl) or Sylvite (KCl). In the connnercial beneciating processes Vin which various products, for example potash and magnesium' compounds, are obtained as the principal products or as the by-prcducts of a concentrating, rening or chemical process, it isv not possible to obtain or recover substances which are 100% pure.

For example, a typical by-product liquor or brine which is produced in the Carlsbad, New

Mexico, area may containv the following substances: Y

Per vcent certain minerals nal tion of NewYork Manning, Glencoe, Ill., Miner-als & Chemical eine* of the general character india brine or liquor to consist of three main steps catedV may be said or stages.V f

- The first of these stages consists in the elimination of undesirable substances, such as sodium or sulphates in the s olid phase, or at least enough of these substances so that they will not be carried forward in the brine to the subsequent steps ofthe process infa'sufiicient amount to interfere K 6.03 Mg 3.65 Na 0.96 C1 13.92 S04 4.99 H2O '70.45

This invention will be described as applied to the production Vof a relatively pure solution. of

MgCl2 from a liquor containing the above-mentioned substances.

in general, it may bestemd that the mention liquor from which with the production of an end lproduct having the desired degree o f purity.

The secondstageY ofthe process may be said to consist in the production'of substantially pure crystals of Carnallitev (YKCLMgClaGI-IzO') from the the objectionable substances have'been largely removed inthe rst stage of the process. l

'The third stage of the process consists in formingY the magnesium chloride solution from the Carnallite crystals and water, preferably by a relatively simple leaching operation, and the subsequent separation of the magnesium chloride in the form of a relatively pure concentrated solution, as an end product of the process.

As an incident'to the q process, various' ley-products are formed, which lay-products mayr be returned to the systemor may be otherwise disposed of, it being understood that the primary object oi they-present process is theV production of as large a percentage of pure magnesium chloride solution as possible from the feed liquor.

in order to assist in describing and understandingf the various Yfeatures of the complete process, we have'prepar'ed certain drawings', which accompany this application.

In said drawings,` l Y Y Y Fig. 1 is a flow sheet of the entire process;

Fig. 2 is'a phase diagram useful in understanding the rst two steps of the process as above described;

Fig. 3 is a phase dlagram'pertaining to the third stage of the process as above described; and

Fig. 41s a .chartshow-ing the composition of the at a relatively lowy temperature so as to eliminate a substantial amount ofV water. Then the tem- Y perature is raised. liquor is ,further concentrated .by evapofrl, tion. At this point in the yvstals of materials process', there are .formed or 6 6- such .as,l.,langl)sinite, also chlorides of potassium practice of the entire 3 and sodium, the percentage of these other substances depending, of course, upon the composition of the feed liquor. Concentration by evaporation is then continued at a higher temperature, and at this zone of higher temperature and concentration, crystals of other materials come out of solution, for example Kieserite and some Carnallite, together with crystals of other materials, and usually a little Halite.

The crystals formed in the final concentrationV of the original liquor could be discarded, but if, as in the present process, it itsu desirable to save as much magnesium as possible, the discarding of the crystals at this stage would result in disf carding a molecule of magnesium with each molecule of sulphate, in view of the Afactthat most of the sulphate crystallizs out as Kieserite (lidgSOiHzO). Therefore, preferably thecrystals formed in the final concentration are settled to a dense slurry and-returned to a lprior stage of the process, where the VKieserite is converted into Langbeinite under favorable conditions, and, when these salts formed in the prior stage are separated and discarded, one-third of the magnesium will be retained in solution as compared with the elimination of the sulphate in the form of Kieserite.

The strong, hot liquor resulting from the final concentration and the removal of the Kieserite in the form of a slurry, is ltered to remove all of the suspended solids. A solution of KCl is then added to the clear liquor and the total solution thus formed is cooled, preferably in a vacuum cooler in whichvsome water is evaporated during the cooling cycle. Thepurpose of adding the KCl solution is to supply a sufficient amount of potassium to assure the maximum production of Carnailite crystals and to supply a sufficient amount of water to retain the sulphates in solution, it being understood that, in this type of process, it is not always possible to obtain complete elimination of undesirable materials by a simple, single crystallization'stage.

After the liquor has been diluted as stated, it is cooled and concentrated under vacuum as a result of which relatively pure crystals of solid Carnallite are formed. After this cooling has proceeded to the desired point, the liquor is recycled back to the system, preferably being combined with the feed liquor. 4The solid Carnallite crystals which then contain the desired magnesium which is to appear in the end product constitute the feed for the final stage of the process.

In the third or final stage of the process, the

Carnallite crystals formed in the prior or second 55 stage of the process are leached with pure water, at a relatively low temperature, so that there are formed crystals of potassium chloride in a magnesium chloride solution. These crystals of potassium chloride are separated from the liquor and may be used in part in a prior stage of the process or may be otherwise disposed of.

Preferably, after the potassium chloride crystals have been separated from the solution, the latter is heated and concentrated, during which stage there may be formed crystals of Carnallite and possibly small quantities of other undesired substances, possibly also small percentages of magnesium chloride, according to conditions.

The hot, concentrated liquor, together with any crystals which may have formed, is cooled, preferably in a vacuum crystallizer, so as to separate as completely as possible the KCl in the form of Carnallite. The crystals are then removed by filtration from the' strong liquor, which is the end product of the process.

If it is desired to use magnesium chloride as a raw material for electrolytic cells in the production of magnesium metal, it will of course be obvious that it is necessary to convert the solution into solid form' by any appropriate dehydration method, for example, by spray drying or otherwise.

Specific example The particular example of the complete process referred to in the drawings is based upon the Y treatment of feed liquor having substantially the Carlsbad by-product liquor above referred to, which is delivered to theI into the No. 2 effect, where a liquid temperature of about C. is maintained. At this point in the operation, water is evaporated at the rate of about 2366 lbs. per hour of operation.

From the effect of the evaporator, (see which at that time contains crystals ofVLangbeinite (2MgSO4-KzSO4), Sylvite (NaCl), is delivered into the shown in Fig. 1, and the clear liquor from the No. 1 settler is then introduced into the high temperature of the No. 1 effect of the evaporator, the liquor being maintained at a' temperature of about 125 C. At this point in the system 3348 lbs. of water per hour are removed.

From the No. 1 effect, the liquor which, as shown in Fig. 2 of the drawings, at that time contains crystals of Kieserite (MgSO4-i-I2O), Carnallite (KCl.MgCl2.6H2O), and Halite (NaCl) is deliveredto the No. 2 settling tank.

The phase diagram, Fig. 2, shows the crystalline Acompounds which are formed in the comp lexV brine underV various temperature conditions and under various concentrations of magnesium ion, measured as magnesium chloride. It is clearly evident from the phase diagram that Langloeinite (2MgSO4-K2SO4) will orystallize out of the solution and Kieserite (MgSO4-H2O) will crystallize out of the solution. The rst mentioned conditions, Langbeinite crystallizing out and Kieserite remaining in solution, occur .in the No. 2 effect and the second mentioned conditions, wherein Kieserite and some maintained in the Carnallite crystallizes out, are y No.\ 1 effect. Thus, crystals may be recycled into the No. 2

of Kieserite which (MgSO4-H2O) willi remain in solution when the temperature of the C. and the concentra- YWhen the .con-

70 C., Kieserite effect from the No.l

1 effect. will be dissolved in the liquor in the ANo.2 effect. 1

From the No. 2 settling tank the clear liquor, most of the non-aqueous constituents foi' which may be representedby-the'formula for Carnallite, is then delive ed to a mixing tank, (see Figli). A

At this point in the process there is added to the clear CarnalliteliquorY a quantity of potassium chloride and va considerable Vvolume of cold water. rlhe amounts of the various substances which are put into the mixing tank areas shown in the circle on Fig. 4. By the time thorough mixing-of the clear liquor and the KCl solutionhas been effected, the temperature of theliquor hasbeen reduced to about 80 C. From the 'mixing tank the Vliquor isv discharged into the No. 1 vacuum crystallizer where the liquor is cooled rby evaporation to a temperature of about C.` 'At this point, water is evaporated at the `rate of about 865 lbs. per hour, (see Figa).

The slurry formed in the No. 1 vacuum crysV tallizer is then delivered to the No. 1 filter where the crystals, which are almost pure Carnallite, are separated, and are fed to the next stage of the process.

These solid Carnallite crystals are charged into the leach tank which is at the same temperature, 25 C., as the No. 1 vacuum crystallizer previously referred at the rate of about '793 lbs. per hour is introduced. When the Carnallite crystals dissolve in the cold water the MgCl2 part of the C'arnallite formula stays in solution but the KCl part immediately recrystallizes, so that the liquor in the leach tank is in the form of a slurry which contains substantially pure crystals of KCl in a substantially pure solution of MgCl2. This slurry is delivered to the No. 2 filter which separates the clear liquor from Vthe crystals. The clear MgCl2 liquor is then delivered to an Ozark evaporator where it is heated to a temperature of about 110 C. and further concentrated. The concentrated liquor flowing from the Ozark evaporator together with any salts which may have come out is then delivered to the No. 2 vac'- uum crystallizer where it is then cooled to a temperature of about 25 C. Any crystals which have been formed are then removed by No. 3 filter so as to produce clear liquor which is a virtually pure solution of MgCl2, the desired end-product of the process.

to, and at this point cold water In order to obtain as high a yield as possible Y in respect of magnesium recovery, it may be and usually is advantageous to re-cycle certain of the side products resulting from the various treatment stages which have been described. For example, in the third or leaching stage of the process, the solid crystals separated from the concentrated end-product in filter No. 3, which consist largely of Carnallite, are returned to the leach tank.

Part of the potassium chloride crystals which constitute the lcake from the No. 3 filter at this third stage are used to supply the potassium chloride which is added to the mixing tank in the previous Carnallite or second stage of the Y process. Y

Also, it is advantageous to save the lclear Carnellite mother liquor which flows from the No. 1 iilter in the Carnellite stage, this mother liquor being added to the raw feed liquor which ows into the rst evaporator (the No. 3 eiect).

Smiilarly, the slurry constituting the undery Mg. in the form of flow from theNo. 2 settler in the Carnellite stage,

isreturnedto the intermediate evaporating stage` As previously stated, the

in the No. 2 effect. purpose of thisis to avoid the discarding .of

nesium. Y Y

The underflow kfrom the No. 1 settler is conducted to a centrifuge which separates the solids from the clear liquor and the clear liquor is also re-cyled back into the No. 2 effect. The solids |coming from the centrifuge, the composition and quantities of whichzare shown in the .drawings as icy-product salts recovered, (see Fig. 4) pass out of the system at this point. These by-product salts may be sold as such or may to produce more valuable substances. The other valuable :by-product of the combined Voperation consists of the unused part of the potassium chloride whichis produced as a cake from Athe No. 2 filter which handles the slurry from the leach tank. Y, I. We, claim: Y Y 1., The improvementv in the rart of removing undesired sulphate ions from an aqueous solution containing magnesium, potassium, chloride, and sulphate ions which comprises: evaporating water from the solution Yunder conditions such that the solution passes through a phase in which Langbeinite will crystallize out of solution and Kieserite will remain in solution, said evaporation being lcarried on at a temperature of at least about 60 C. and at a concentration of magnesium ions, measured as magnesium chloride, such that there are less than about 80 mols of magnesium chloride per 1000 mols of water; and separating Langbemite crystals 'from the solution while maintaining the solution at the aforesaid conditions. Y

2. The improvement in the art of removing undesired sulphate ions from an aqueous solution containing'magnesiimn, potassium, chloride, and sulphate ions which comprises: first, evapoating water from the solution under conditions such that the solution passes through a phase in which Langbeinite will :crystallize out of solution and Kieserite will remain in solution, said evaporation being `carried on at a temperature of at least about 60 C. and at a concentration of magnesium ions, measured as magnesium chloride, such that there are less than about 80 mols of magnesium chloride per 1000 mols of water, separating Langbeinite lcrystalsfrom the solution while maintaining said solution at the aforesaid conditions; evaporating lwater from the resultant liquor until the concentration of magnesium ion, measured as magnesium chloride, is over about 80 mols of magnesium chloride per 1000 mols of water, maintaining the temperature of the liquor over about '707 C. and separating the Kieserite crystals, which are'formed, from the solution; and finally recycling the separated Kieserite crystals toY the first evaporation step so that the Kieserite crystals become dissolved and Langbeinite crystals are fonmed, therebyreffecting the removal of sulphate ions from the solution as Langbeinite.

3. The method of recovering sulphate free mag- Y Y said evaporation being carried out at a temperature over about 60 C. and a `concentration a simple sulphate of magr be beneficiated` of 'magnesium ions, measured as magnesiumchlo-- ride, such that there are less than about 80 mols of magnesium chloride per 1000 mols of water, separating Langbeinite crystals from the solution while maintaining said solution at the aforesaid' conditions; evaporating water from the resultantV water. maintaining the temperature of the liquor' over about '70 C. and separating the Kieserite crystals which are formed from the solution; recycling the separated Kieserite crystals into the Zone of the first evaporation so that the Kieserite crystals become dissolved and Langbeinite crystais are formed; mixing a potassium chloride solution with the liquor from which the Kieserite has been removed, evaporating Water from the r sulting solution at a temperature of about 25 C., whereby Carnallite crystals are formed; removing the Carnallite crystals from the liquor; recycling theCarnallite liquor to the rst evaporation step; leaching said Carnallite crystals with REFERENCES CITED The-following referencesv are of record in the le of this patent: Y

UNITED STATES PATENTS Y Number Namev Date 1,304,097' Reeve May 20, 1919 1,305,566 Reeve June 3, 1919 OTHER REFERENCES Seidell, Solubilities of Inorganic and Organic Compounds, vol. f1, page 641 (1919), and vo1.'2, page 1283 (1928) pub. by D'. Van Nostrand Co., N. Y. 

